(1) Field of Invention
The present invention relates to an electrophotographic copying process for obtaining a reversed image (positive) of a negative using pressure fixing of a pressure-sensitive development powder (toner). More particularly, the present invention relates to a process for developing an electrostatic latent image by depositing a pressure-sensitive development powder on the uncharged areas (neutral areas) wherein the resulting positive reproduction is fixed by passing the developed image between pressure rollers.
(2) Discussion of the Prior Art
The reversed development of an electrostatic latent image is necessary when it is desired to reproduce a positive reproduction from a negative image or transparency. For example, reverse development is used in microfilm reader/reproducer machines. In reversed development processes, the development powder or toner is deposited in the uncharged or electrically neutral areas. Most typically, fixing of the development powder is accomplished by application of heat whereby the resin material of the development powder melts and becomes fixed or adhered to the copying paper. Images of good quality have been obtained by this procedure.
More recently, much effort has been devoted to fixing of the development powder by application of pressure. Pressure fixing has the advantage of being simple since it is merely necessary to provide metal rollers not requiring any complex procedures for their machining to a satisfactory surface condition.
Moreover, pressure fixing has the advantage that if the copying paper becomes jammed between the rollers, no likelihood of overheating or initiation of a fire results. This is in contrast to apparatus in which fixing is accomplished by heat, in which jamming of the copying paper can result in a fire in the machine.
Although apparatus using pressure fixing or reversed developed electrostatic latent images have been provided using metal rollers for the fixing, it has been observed that the resulting copies were of generally poor quality with regard to lack of sharpness and definition of the image.